This invention relates to a guide wire. More particularly, the invention relates to a guide wire of excellent follow-up characteristics having sufficient X-ray contrasting characteristics and flexibility at a distal end portion of the guide wire, and high elasticity at a proximal end portion of the guide wire.
In order to examine and remedy an affected part of the vascular system, a catheter has been introduced into a blood vessel or a vascular cavity other than a blood vessel. A guide wire is used for the introduction of such a catheter into the vascular cavity. For example, in a percutaneous transluminal coronary angioplasty (PTCA), a guide wire is inserted through an expansible catheter provided with a balloon at a distal end of the catheter. This guide wire is made to reach an objective constriction as a objective branch of a coronary artery is selected under a radioscope. The guide wire is further forced into the constriction and passed therethrough. The catheter is thereafter introduced into the constriction along the guide wire so as to position the balloon in the constriction, the constriction being expanded by expanding the balloon.
A guide wire is desired to have torque communicability so that a distal end of the guide wire can face in a desired direction so as to allow the guide wire to reach an objective part. The torque communicability is an ability such that when the guide wire is turned by hand, a resultant turning force is transmitted to a distal end of the guide wire. A guide wire introduction operation is carried out with exposure of the guide wire to an x-ray as a position of a distal end of the guide wire is ascertained, so that the distal end of the guide wire needs to have X-ray contrasting characteristics. In order to further advance the guide wire into a vascular cavity which branches in a complicated manner, the guide wire needs to have a flexibility (follow-up characteristics) which permits the guide wire to be transformed following up a shape of the vascular cavity.
A guide wire including a core wire having a distal end portion and a proximal end portion, and a coil wire provided so as to be wound around the distal end portion of the core wire has been proposed (Publication WO99/65558, Japanese Patent Laid-Open No. 38210/1997, etc.). Each of these guide wires has excellent torque communicability, excellent X-ray contrasting characteristics of the distal end portion of the guide wire and excellent follow-up characteristics.
In the guide wire disclosed in the publication of WO99/65558, one of an inner layer and an outer layer of a coil wire is formed of a radiation impermeable material, and the other layer is formed of a material of high strength. Suitably selecting a ratio of the materials gives a distal end of the guide wire flexibility and excellent X-ray contrasting characteristics. The guide wire disclosed in Japanese Patent Laid-Open No. 38210/1997 uses a coil wire formed by butt welding ends of a radiation impermeable wire rod and a radiation permeable wire rod together, reducing a diameter of the resultant product and drawing out a length thereof to obtain a single extra fine element coil wire, and winding this element coil wire. This guide wire enables itself to be inserted into a micro blood vessel owing to a smooth and uniform bent shape of the guide wire.
Each of these related art guide wires is formed by combining a wire rod of a material having high contrasting characteristics and a wire rod of a material of high elasticity with each other by a method including welding and the like so as to give the final coil wire properties of both excellent contrasting characteristics and high elasticity, reducing a diameter of the resultant wire rod and drawing out a length thereof to obtain a single wire, and winding this wire. Therefore, it has been difficult to gradually increase the elasticity of the coil wire toward the proximal end thereof.